diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/Extensions/DefaultTagHelperOptimizationPassTest.cs b/test/Microsoft.AspNetCore.Razor.Language.Test/Extensions/DefaultTagHelperOptimizationPassTest.cs
new file mode 100644
index 0000000000..5808681766
--- /dev/null
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/Extensions/DefaultTagHelperOptimizationPassTest.cs
@@ -0,0 +1,128 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System.Linq;
+using Microsoft.AspNetCore.Razor.Language.Intermediate;
+using Xunit;
+
+namespace Microsoft.AspNetCore.Razor.Language.Extensions
+{
+    public class DefaultTagHelperOptimizationPassTest
+    {
+        [Fact]
+        public void DefaultTagHelperOptimizationPass_Execute_ReplacesChildren()
+        {
+            // Arrange
+            var codeDocument = CreateDocument(@"
+@addTagHelper TestTagHelper, TestAssembly
+<p foo=""17"" attr=""value"">");
+
+            var tagHelpers = new[]
+            {
+                TagHelperDescriptorBuilder.Create("TestTagHelper", "TestAssembly")
+                    .TypeName("TestTagHelper")
+                    .BoundAttributeDescriptor(attribute => attribute
+                        .Name("Foo")
+                        .TypeName("System.Int32")
+                        .PropertyName("FooProp"))
+                    .TagMatchingRuleDescriptor(rule => rule.RequireTagName("p"))
+                    .Build()
+            };
+
+            var engine = CreateEngine(tagHelpers);
+            var pass = new DefaultTagHelperOptimizationPass()
+            {
+                Engine = engine
+            };
+
+            var irDocument = CreateIRDocument(engine, codeDocument);
+
+            // Act
+            pass.Execute(codeDocument, irDocument);
+
+            // Assert
+            var @class = irDocument.FindPrimaryClass();
+            Assert.IsType<DefaultTagHelperRuntimeIntermediateNode>(@class.Children[0]);
+
+            var fieldDeclaration = Assert.IsType<FieldDeclarationIntermediateNode>(@class.Children[1]);
+            Assert.Equal(bool.TrueString, fieldDeclaration.Annotations[CommonAnnotations.DefaultTagHelperExtension.TagHelperField]);
+            Assert.Equal("__TestTagHelper", fieldDeclaration.FieldName);
+            Assert.Equal("global::TestTagHelper", fieldDeclaration.FieldType);
+            Assert.Equal("private", fieldDeclaration.Modifiers.First());
+
+            var tagHelper = FindTagHelperNode(irDocument);
+            Assert.Equal(5, tagHelper.Children.Count);
+
+            var body = Assert.IsType<DefaultTagHelperBodyIntermediateNode>(tagHelper.Children[0]);
+            Assert.Equal("p", body.TagName);
+            Assert.Equal(TagMode.StartTagAndEndTag, body.TagMode);
+
+            var create = Assert.IsType<DefaultTagHelperCreateIntermediateNode>(tagHelper.Children[1]);
+            Assert.Equal("__TestTagHelper", create.FieldName);
+            Assert.Equal("TestTagHelper", create.TypeName);
+            Assert.Equal(tagHelpers[0], create.TagHelper, TagHelperDescriptorComparer.CaseSensitive);
+
+            var property = Assert.IsType<DefaultTagHelperPropertyIntermediateNode>(tagHelper.Children[2]);
+            Assert.Equal("foo", property.AttributeName);
+            Assert.Equal(AttributeStructure.DoubleQuotes, property.AttributeStructure);
+            Assert.Equal(tagHelpers[0].BoundAttributes[0], property.BoundAttribute, BoundAttributeDescriptorComparer.CaseSensitive);
+            Assert.Equal("__TestTagHelper", property.FieldName);
+            Assert.False(property.IsIndexerNameMatch);
+            Assert.Equal("FooProp", property.PropertyName);
+            Assert.Equal(tagHelpers[0], property.TagHelper, TagHelperDescriptorComparer.CaseSensitive);
+
+            var htmlAttribute = Assert.IsType<DefaultTagHelperHtmlAttributeIntermediateNode>(tagHelper.Children[3]);
+            Assert.Equal("attr", htmlAttribute.AttributeName);
+            Assert.Equal(AttributeStructure.DoubleQuotes, htmlAttribute.AttributeStructure);
+
+            Assert.IsType<DefaultTagHelperExecuteIntermediateNode>(tagHelper.Children[4]);
+        }
+
+        private RazorCodeDocument CreateDocument(string content)
+        {
+            var source = RazorSourceDocument.Create(content, "test.cshtml");
+            return RazorCodeDocument.Create(source);
+        }
+
+        private RazorEngine CreateEngine(params TagHelperDescriptor[] tagHelpers)
+        {
+            return RazorEngine.Create(b =>
+            {
+                b.Features.Add(new TestTagHelperFeature(tagHelpers));
+            });
+        }
+
+        private DocumentIntermediateNode CreateIRDocument(RazorEngine engine, RazorCodeDocument codeDocument)
+        {
+            for (var i = 0; i < engine.Phases.Count; i++)
+            {
+                var phase = engine.Phases[i];
+                phase.Execute(codeDocument);
+
+                if (phase is IRazorDirectiveClassifierPhase)
+                {
+                    break;
+                }
+            }
+
+            return codeDocument.GetDocumentIntermediateNode();
+        }
+
+        private TagHelperIntermediateNode FindTagHelperNode(IntermediateNode node)
+        {
+            var visitor = new TagHelperNodeVisitor();
+            visitor.Visit(node);
+            return visitor.Node;
+        }
+
+        private class TagHelperNodeVisitor : IntermediateNodeWalker
+        {
+            public TagHelperIntermediateNode Node { get; set; }
+
+            public override void VisitTagHelper(TagHelperIntermediateNode node)
+            {
+                Node = node;
+            }
+        }
+    }
+}